Just about aluminum extrusion
Why extrusion
Aluminum, really, extruded from the container through the press die aperture, which is formed on the aluminum profile section. Direct meaning of the English word "extrusion" just means "squeezing".
Aluminum alloys for extrusion
The vast majority of extruded aluminum profiles are made from 6xxx series alloys.. The basic alloying elements of the alloys - magnesium and silicon in an amount up to 1,2 %. Of all 6xxx series alloys the most popular are international alloys 6060 and 6063, which are analogues of domestic alloy AD31. These alloys are thermally hardening, i.e. it has the ability to improve their strength as a result of thermal treatment. About profiles of these alloys will, primarily, discussed below.
Ingot-logs
The starting material is aluminum ingots for the production of aluminum profiles. Most often, they have the form of cylindrical columns up to 7 m (figure 1). These logs may have different diameters, usually, in one inch increments (25.4 mm). The most common are the logs with a diameter of 6 inches to 9 inches (from 152 to 228 mm). About the process of making ingots-logs (casting and homogenization) see. here.
Figure 1 - Cutting ingots of pillars into blanks [1]
Billet
The press container was charged with the whole not pillar, and part of it - blank. Part manufacturers advance profile desired length is cut from the workpiece pillars - typically from 400 to 1000 mm (cm. Figure 1), others - into the furnace full post, and then immediately before loading into the press cut away a heated preform of desired length.
Heating of the billet
The figure 2 shows a feeding process in advance the cut billet in a heating furnace blanks. Preform enters the furnace and is heated to a predetermined temperature.
Figure 2 - Heating the billet before extrusion [1]
The melting point of pure aluminum is 660 oC. With increasing content of impurities and alloying elements of aluminum alloys the temperature, which are used for the manufacture of profiles is slightly reduced (see. more here). A typical temperature of the preform of the 6xxx series alloys before loading into the press is between 400 to 480 oC. The exact heating temperature depends upon the chemical composition of the alloy, the complexity of the profile and other parameters.
Note, that the heated blank does not visually different from cold, it does not have a reddish tint and is not lit..
Matrix heating and installing it on the news
For pressing a predetermined profile corresponding matrix prepared - it is heated in matrices heating furnace to a temperature close to the temperature the preform.
Figure 3 - Installation of the matrix set in the press [1]
Application of lubricant on the end of the workpiece
The heated preform is removed from the furnace and sent to a press for loading into the container. Before the loading of the press at the rear end of the blank is applied lubricant layer, which prevents sticking of the press washer on the workpiece at the return movement of the ram at the end of the pressing cycle,. Typically, this end of the workpiece is directed to the burning acetylene torch. Formed by incomplete combustion of acetylene soot preform end covers and plays a role of the lubricant itself.
Figure 4 - Feeding the workpiece to the press and applying grease to its rear end [1]
Loading preform into a container and compressing
Harvesting freely "pushed" the ram in a container, of which the diameter 3-4 mm longer, than the diameter of the workpiece. Then the ram begins to "push" on the end of the workpiece with great force, so that the preform material fills the entire volume of the container. With further advancement of the ram pressure in the container increases, and aluminum begins to "squeeze out" through the holes of the matrix in the form extruded profile with a given cross section (figure 5).
Figure 5 – Loading the blank into the container and extruding the profile [1]
Butt
At the end of the blank about the press cycle 10 % its volume, including its outer shell, remains in the rear part of the container. Container slightly pulls back, and this part of the workpiece is removed from the container and cut by a special matrix-sharp knife guillotine. This severed portion of the preform is called press residue. He, along with other technological waste is sent to be melted.
Extrusion speed
Profile exits the die at a temperature above 500 oC. Speed motion profile at the outlet of the matrix may be from 8 to 80 m per minute depending on the alloy and the complexity of the profile (figure 6). The longitudinal profile of the transfer of the receiving table, which can reach lengths 50 m, usually involved puller. It captures with special clamps the front end profile and pull the profile of roller bed of the table. Travel speed puller and thrust, which he has made to the profile, aligned with the exit velocity profile of the matrix.
Figure 6 - Profile exit from the matrix;
cooling profiles on the outlet table [1]
Tempering in the press
Almost immediately after the release profile of the matrix is typically subjected to accelerated cooling to, aluminum alloy profile that has reached tempered condition – hardening on press.
To achieve quenching state, each alloy has its lowest permissible cooling rate to a temperature of about 250 oC. for instance, alloy profiles 6060 should not reach this temperature, more, than five minutes. For thin-walled profiles that may be enough cooling fans on the receiving table. For profiles of more doped alloy 6082 typically requires increased cooling compressed air, water-air mixture or even water immediately after leaving the matrix (see. Figure 6).
Aluminum hardening and tempering steel
Hardening aluminum alloys differs from tempering steel. Steel immediately after cooling dramatically increases its strength. Aluminum alloys after quenching is practically not change their strength. hardening effect appears only as a result of the subsequent aging step - natural or artificial. Natural aging - a normal maturing this mass at room temperature for several weeks or even months. Hence the term "aging".
Hot cutting profiles
Profile Length, which is pressed from a single blank, can reach 50 m. It depends on the dimensions of the workpiece (diameter and length) and the cross-sectional area of the profile, as well as the length of the table press. Usually at the end of each pressing cycle, this continuous profile are cut long hot saw cutting of that portion of the profile, which is still in the matrix (figure 7). This profile is then transmitted to the table cooling profiles.
Figure 7 - Hot cutting saw [1]
Table cooling profiles and stretching machine
On the cooling table profiles continue their cooling to workshop temperature and then applied to tenter (Figure 8). At tenter stretching profile is subjected to a predetermined amount of plastic deformation. The purpose of this operation - reducing the shape of the profile deviations from straightness and twisting, and, if necessary, predetermined cold deformation.
Figure 8 - Profiles on the cooling table and in the stretching machine [1]
Cold cutting saw
After the stretching machine, the profiles go along the roller table to the dimensional cutting saw (Figure 8). This saw is also called a cold cut saw, in contrast to hot cutting blade on the output table press. It profiles are cut to length according to customer requirements, usually 2 to 6 m. Profiles of measured length are placed in special steel baskets and, depending on the purpose (and type of alloy), are sent to the packaging area or to the aging oven.
Figure 9 - Saw for dimensional cutting [1]
Aging furnace
The profiles of heat-strengthened alloys, such as Alloy 6060, reach their maximum strength in, which is called hardening of aging. The aging of the alloying elements of the alloy, that as a result of tempering were "frozen" in a solid solution of aluminum, precipitated as fine particles. This leads to an increase in the strength properties of the profiles.
This aging process can occur at room temperature for several weeks or even months. In this case, it is called the natural aging. The maximum increase in strength properties is achieved by artificial aging, which is produced by heating in a special oven – aging furnace (Figure 10). Typical alloy mode 6060: temperature 180 º C and duration 5 hours.
Figure 10 – Loading profiles into the aging furnace [1]
Wrapping, warehousing and shipping
Finished aluminum profiles are transferred to:
- for powder painting or anodizing;
- for packing and shipment to the customer;
- to the warehouse (figure 11).
Figure 11 – Packaging and storage of aluminum profiles [1]
Source of pictures:
http://www.abralco.com/index.php/about-aluminium/aluminum-extrusion
See more details:
Aluminium Extrusion Technology – R. Saha
Extrusion of Aluminium Alloys – T. Sheppard
